Branching morphogenesis of the lung is controlled by well-orchestrated signaling cascades between the developing epithelial and mesenchymal compartments. However, the complex transcription factor interactions that regulate lung epithelial differentiation remain poorly understood. Thyroid transcription factor 1 (TTF1) and GATA6 have been implicated in differentiation of the distal pulmonary epithelium and we have clearly shown that Nuclear Factor I (NFI) regulates surfactant protein-C gene expression. We also identified NFI binding sites in the promoters of several other lung epithelial specific genes. Our preliminary data suggests that NFI interacts with both TTF1 and GATA6 and is critical for proper lung development and Type II cell maturation. All NFI family members are expressed in adult Type II cells, however genetic inactivation of Nfib, but not Nfia, causes neonatal death by respiratory failure due to a block in lung maturation. This proposal will test the hypothesis that NFIB coordinates the interaction of other transcription factors and cofactors to regulate distal lung morphogenesis, proliferation, and Type II cell specific gene expression. We hypothesize that NFI plays a major role in inhibiting cell proliferation during cytodifferentiation and in the adult lung. The goals of this proposal are to 1) determine the role of NFI in pulmonary epithelial cell proliferation and differentiation in vivo and in vitro using doxycycline regulated overexpression and "dominant-repressor" strategies; 2) determine whether epithelial expression of a single isoform of Nfib in Nfib gene targeted mice is sufficient to induce progression of lung development and distal epithelial cytodifferentiation; 3) identify the protein-protein interactions that modulate NFI transcriptional activity in Type II cells. The current proposal will define novel molecular mechanisms by which NFI regulates epithelial cytodifferentiation and morphogenesis of the developing lung. These studies may provide a basis for the rational design of new treatment strategies for neonatal pulmonary disease and bronchopulmonary dysplasia. [unreadable] [unreadable]